1. Field of the Invention
This invention relates to a semiconductor laser apparatus and more particularly to improvement of the optical system in the laser apparatus.
2. Description of the Prior Art
Referring to FIG. 1, there is shown a sectional view of a prior art laser apparatus. A semiconductor laser chip 1 is attached to a side wall of a block 8 which is fixed on the top surface 5a of a stem 5. The stem 5 is provided with an electrode 3 which is connected to the laser chip 1 through a bonding wire 6a. Both end faces 1a, 1b of a resonator in the laser chip 1 are substantially parallel to the top surface 5a of the stem 5. The upper end face 1a in the laser chip 1 is provided with an antireflective coating, while the lower end face 1b is provided with a reflective coating. A strong laser beam 9a is emitted upward from the upper end face 1a and another weak laser beam 9b is emitted downward from the lower end face 1b. Various characteristics of the semiconductor laser can be controlled by controlling the reflectance of each of the end faces 1a, 1b of the resonator. Also fixed on the surface 5a of the stem 5 is a mount to which a photodiode 2 is attached. The stem 5 is provided with another electrode 4 which is connected to the photodiode 2 through another bonding wire 6b. A major surface 2a of the photodiode 2 is to receive the weak laser beam 9b. and makes a certain angle with the top surface 5a of the stem 5.
In operation, the strong laser beam 9a emitted from the upper end face 1a in the chip 1 is offered for practical use, while the other weak laser beam 9b emitted from the lower end face 1b is directed to the photodiode 2. The intensity of the strong beam 9a can be estimated by monitoring the intensity of the weak beam 9b with the photodiode 2, because the intensity of the strong beam 9a is proportional to that of the weak beam 9b.
Since the prior art laser apparatus is structured as described above, there exists a problem that when the reflectance of the reflective coating on the lower end face 1b is increased in order to change the laser characteristics, the weak laser beam 9b is further weakened and thus enough photoelectric conversion output can not be obtained from the photodiode 2. Further, since the laser chip 1 is set vertical to the top surface 5a of the stem 5, there exist another problem that assembling of the laser apparatus is rather complicated.